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Evolutionary psychology is a new way of thinking about - human behaviour - my student's will be relieved to hear that rats don't get much of a look-in during this lecture!
Evolutionary psychology can be applied to any topic that is studied by psychologists. It is built upon the rock of Darwin's theory of evolution published in 1859. We usually associate Darwin with the evolution of structure and function, but Darwin suggested that evolution acted on patterns of behaviour as well as the anatomy and physiology of the body. He believed that human behaviour would eventually be explained in terms of evolutionary principles.
Biology is built upon the foundations provided by Darwin's theory of evolution. In contrast, psychology rests on the Standard Social Science Model . This model contains the barely concealed idea that human behaviour is guided by reason , whereas non-human animal behaviour which is influenced by instinct . According to the Standard Social Science Model the human mind is blank at birth (a tabula rasa - blank slate) and is filled as the result of experiences during the individual's lifetime. Behaviourism is a classic example of this approach to understanding human behaviour.
The idea that human behaviour is based on instincts was popular with psychologists about 100 years ago. [Incidentally, the best place to read about the decline of this idea, and the rise of behaviourism is Boakes ' From Darwin to behaviourism ', Cambridge University Press, Cambridge, 1984) see also Daly & Wilson (1999) ]
In 1975 E.O. Wilson wrote a groundbreaking and challenging book ' Sociobiology the New Synthesis ' in which he argued that human social behaviour could be explained in evolutionary terms. This caused an outcry in many quarters. Alcock (1998) provides a useful summary of the debate. I think it is always worth bearing in mind that Sociobiology (or any other approach ) is merely a theory . A theory has a purpose - to explain a body of knowledge and suggest directions for further investigation.
A theory is a bit like a Swiss army knife. It contains a number of useful tools. But eventually it wears out, or you need a tool that is not provided. But of course - in the wrong hands - you can be killed by a Swiss army knife ....
Nicky Hayes provides a very clear critique of the concepts underlying Sociobiology. One of the reasons why Sociobiology generated so much intellectual heat is the memory of what occurred in the past when evolutionary theories were presented in 'watered-down' or distorted versions to the general public.
Social Darwinism is a prime example. Social Darwinism emphasized evolution based upon "survival of the fittest" and painted a picture of "Nature red in tooth and claw". This view of evolution could be used to support oppressive economic policies and racial discrimination. This way of thinking about people can end up in mass extermination camps where genocide, compulsory sterilization, and breeding programmes, are used to ensure racial purity.
The term Sociobiology has now been replaced by the term evolutionary psychology . A good place to begin reading about this new area is Cosmides and Tooby Evolutionary Psychology: A Primer which is available online.
Cosmides and Tooby argue that psychology is a branch of biology. To some of you this may appear to be 'a self-evident-truth'. Others may not have thought about this, or reject it immediately. But the relationship between biology and psychology is an important issue, and one that you should form an opinion about.
Evolutionary psychologists believe that behaviour is strongly influenced by inherited factors, and that every human being acts (consciously, but mostly unconsciously) to enhance their inclusive fitness - i.e. to increase the frequency and distribution of their genes in future generations. As Steven Pinker puts it, 'the ultimate goal that the mind was designed to attain is maximizing the number of copies of the genes that created it'.
Cosmides and Tooby describe the principles that guide an evolutionary psychology approach to any topic within psychology:
Boaz and Almquist (1999) provide a detailed account of human evolution. You may find it useful to view the video "The First People" which shows how rock paintings may give us an insight into the minds of our ancestors .
The overarching concern of evolutionary psychology is to identify factors that maximize reproductive success .
Contemporary psychology is very concerned with measuring and understanding the causes of differences between people. For example, most of you will be carrying out experiments as part of your third year projects specifically designed to manipulate experimental conditions to produce differences between groups of people.
In sharp contrast evolutionary psychologists are particularly interested in psychological mechanisms that:
(See Definition of Evolutionary Psychology )
The debate between The Standard Social Science Model and evolutionary psychology boils down to whether the mind is constructed during development of the individual, or has evolved during development of the species.
In our daily lives we are surrounded by examples of animals that have evolved. One of the reasons for believing in evolution is our own ability to modify animals through selective breeding . For example, Man has selectively bred dogs, cats and farm animals for thousands of years. Clearly there have been changes in the appearance of these animals as a result of domestication . But can behaviour be altered by selective breeding?
In a classic experiment Thompson (1954) trained rats to run through a maze for a food reward. Some rats learnt this task faster than others. Thompson selectively bred fast and slow learners, so that over several generations rats were descended from a line of fast or slow maze learners. Eventually two strains of rats developed - 'maze dull' and 'maze bright'. After only six generations, the maze dull rats made twice as many errors before learning their way through the maze than the maze bright strain of rats.
A baby's brain is very large at birth compared to the size of the rest of the body, and barely fits through its mother's pelvis. The brain continues to grow rapidly during childhood. The adult human brain is four times larger than would be expected in a primate with our size of body.
Human babies have restricted motor capabilities when they are born. For example, it takes a human twice as long as a chimpanzee or gorilla to develop the ability to walk and hold on to its mother.
Babies were part of our ancestors Environment of Evolutionary Adaptedness (EEA) .
Babies represent one of the challenges that our behaviour has adapted to during evolution. It takes a long time for a child to reach a state where it could survive without its parents. Parents input into caring for the child is called parental investment . Parental investment represents a cost for both mother and father. But the production of babies that mature and reproduce are the expression of parents' inclusive fitness.
|Fathers can never be
sure that they actually are the father of the child in which they are
Here is a link to an article from The Times (23rd January 2000) with the headline One in seven fathers 'not the real parent' which suggests that a large number of children are not fathered by the man who believes he is their father.
This startling conclusion is based on results of DNA genetic testing of blood samples from supposed parent and offspring.
Quotation from The Times article:
Do you think these tests were carried out on a random selection of the population? What is the implication of your answer for the conclusion that a large number of children are not genetically related to their 'fathers'?
|Point to ponder: What is childhood for? Seems like a silly question. What's the answer then? Mace (2000) points out that children could grow faster than they actually do grow. What do children learn during childhood that increases their inclusive fitness? Apparently there is no evidence on what this might actually be. Not such a silly question then!|
psychology suggests that males have evolved an approach to mating that
leads them to seek multiple copulatory partners. This prediction is
used to explain the the following observations:
|Source: Buss & Schmidt, Psychological Review , 100, 204-232, 1993|
|A note of caution; These results are based on what men and women say about their desires and preferences. People's replies to questions about what they think they would do should be treated with caution. Researchers need to be wary of demand characteristics influencing participants' behaviour. Demand characteristics refer to participants awareness of experimenters' goals or cultural expectations influencing participants responses. See Mace (2000) for a discussion of this confounding factor in evolutionary psychology research.|
Although there is a sex difference in the attitude of males and females to casual sex, this difference disappears when men and women are asked about the qualities they seek in a partner for a long term relationship . College students were asked about the minimum intelligence they would require in a partner for casual sex. Men, but not women were prepared to have casual sex with a partner of much lower intelligence than women. However, men and women have similar standards for the minimum intelligence that they would accept in a marriage partner.
In this diagram the results are expressed in terms of the percentile intelligence of an acceptable partner. A value of 40 means that the prospective partners intelligence would lie at the 40th percentile - 40% of the population would have lower intelligence. A value of 70 means that 70% of the population would have lower intelligence. Thus a person with a percentile score of 70 is more intelligent than someone with a percentile score of 40 ( Kenrick et al , 1990).
Males and females seem to look for the same psychological characteristics in long-term partners such as : kindness, understanding, intelligence, personality, adaptability, and creativity (Buss and Barnes, 1986).
|On the 28th September
2000, a judge in the United States awarded a former Playboy model, 26
year old Anna Nicole Smith, $449m after she was left out of the will of
her 90-year-old husband.
Ms Smith was 26 when she married J Howard Marshall a Texan oil tycoon who died 14 months after they married.
A lawyer in the case commented: "He's given her cars, a company. He had given incredible things that were intended to help her get ahead and survive and make money" .
The idea that there are fundamental differences between the reproductive strategies of males and females is an example of what evolutionary psychologists call universals . Universals are behaviour patterns that do not vary greatly between individuals.
But this view does not stand up to closer analysis. You have probably seen news reports of strangers who meet on aircraft and engage in sexual behaviour that lands them in court - (e.g The Independent, 6/04/2000, p 9). In the UK there have been several programs showing the behaviour of young people on holiday where there is clear evidence of women as well as men seeking sex with multiple partners.
This diagram shows overlap in the willingness of men and women to have sex with an attractive, healthy and emotionally undemanding stranger ( Symons & Ellis 1989).
Similarly, Gangestad & Simpson (2000) re-examined Buss & Schmitts (1993) report on male and female desire for multiple sex partners discussed above . Clearly the sexes differ on this measure, but there is considerable overlap between the sexes - and variation within the sexes - on the desire to have sex with multiple partners. Thus some women wish to have multiple partners, and some men wish to have relatively few sexual partners. Clearly there are not universal differences between males and females in these behaviours. Why did this variability evolve? Does it make sense in terms of an individuals inclusive fitness? Gangestad & Simpson (2000) suggest that which strategy is adopted may be conditional on other factors in the person's environment.
For example, if a man was relatively unattractive to women, it would increase his inclusive fitness if he helped to raise his children rather than invest time and energy pursuing other reluctant mating opportunities. From a woman's point of view, it may be to her advantage to seek a succession of short-term mates so that her child benefits from their good genes, and a long term mate so that her child benefits from his parental investment. The best strategy thus becomes a matter of the individual carrying out a cost-benefit analysis on each of the sexual strategies at their disposal.
Paternal investment involves giving time and physical resources to a child
|Men and women may have
evolved ways of detecting characteristics in each other that predict
good short-term and long-term mates.
Evolutionary psychology views this decision making process as being unconscious . Remember that one of the principles of evolutionary psychology is that complex behaviours that impact on inclusive fitness are unconscious.
Good short-term mates are men with signs of healthiness and the ability to withstand diseases that will be passed on to the woman's child. This is called good gene sexual selection (GGSS). What are the external signs of good-genes? Currently there is considerable interest in fluctuating asymmetry . This refers to the degree to which a person's features differ between each side of their body. For example, do you have problems finding shoes that fit because one foot is bigger than the other? Are your ears a different shape? These are all examples of asymmetries.
The characteristics valued in long-term mates may include honesty, reliability,loyalty - good parenting qualities. Evolutionary psychologists are interested in the psychology of cheating . Emotions may have evolved as part of our reaction to cheating.
Gangestad & Simpson (2000) suggest that women's decision to seek short or long term mates may depend on environmental circumstances at the time they mate. If the child is going to be born into a world dominated by death and disease it would make sense to mate with a man rich in good genes. On the other hand, if a woman is in an environment where she has difficulty obtaining resources she should favour mating with men of high status and power who exhibit good parenting skills.
Consequently, according to these authors, the environment controls what tactic women adopt - short or long term mating, and men in turn adjust their mating strategy to female demands.
|Point to ponder: "I only want you for your sperm" How would you test the hypothesis that fluctuating asymmetry is associated with human mating behaviour?|
Men rate the following features as attractive in a woman:
These features are associated with a strong immune system, high estrogen level, developmental stability and youthfulness i.e. they signal youth and high fertility.
When women are presented with diagrams of males with waist to hip ratios between 0.7 and 1.0, they preferred the figure with a WHR of 0.9 ( Singh , 1995)
|You probably find the
pictures on the left hand side of this display more attractive than
those on the right. The male and female pictures on the left have been
artificially constructed using a computer which is fed 32 human faces
and averages them to produce an average face. One
explanation for this preference is that the image exploits our
preference for symmetrical faces. Symmetrical
faces are though to signal ' healthiness ' to the
viewer. It strikes me that one effect of the way these faces are
constructed is to remove minor skin blemishes - the spots and wrinkles
we all have. A clear complexion may be a contributory factor in
attractiveness. How would you test this hypothesis?
The odd thing is that 6 month old babies also show this preference for averaged faces. They spent more time looking at the pictures on the left. Evolutionary psychologists use this type of evidence to argue for the presence of universal modules in the human brain that have evolved as part of our mate selection strategy. You can read about this research in Discover 21/2 February 2000 which is available online.
|'Men grow cold as girls grow old'. Kenrick & Keefe ( Behavioural and Brain Sciences , 15, 75-133, 1992) provide evidence that is consistent with the idea that men are looking for youthfulness in their partners, whereas women seek mates who are older and presumably control greater resources. They examiner advertisements in a newspaper placed by men and women who were seeking romantic partners. The advertiser indicated their own age, and the age of the partner they were looking for. As men get older they are looking for younger and younger partners. Women of all ages, on the other hand, were prepared to accept replies from potentipartners 10 years their senior.|
Gangestad & Simpson suggest that women have short-term and long-term mating strategies that are influenced by a male's genetic fitness and his willingness to help in child-rearing.
|Females are a rate-limiting resource which limits male reproductive success. Much human behaviour involves negotiating reproductive contracts between men and women. Parents can influence their reproductive success by facilitating the reproductive success of their own offspring. This is seen in societies in which parents ensure their sons reproductive success by buying them wives and leaving them them resources in the form of inheritances.|
In some societies, the groom and his family transfer resources (labour or goods) to the bride's family. These resources are called bridewealth .
In others, the bride's family gives a dowry to the groom or his family.
Evolutionary psychology predicts that - because males compete for access to females - bridewealth payments should be more common than dowries.
This figure (adapted from Daly & Wilson (Homicide, New York, Aldine, 1988) is a cross-cultural comparison of economic arrangements surrounding marriage and shows that bridewealth is much commoner than dowry payment which is only practised in 22 societies.
Furthermore, bridewealth payment occurs in about 90% of societies where one man marries several women (polygynous societies). In nearly all polygynous societies, the system of inheritance of parents' wealth favours sons over daughters (Alcock, 1998 op. cit. ).
Alcock discuses societies in which parents favour their daughters over sons in terms of giving them dowries and inheritances. This seems to occur in situations where the dowry will secure their daughter a high-status husband who will use his resources to support their grandchildren. Sons are not favoured by these resource-poor parents because the son's reproductive success is less likely. Alcock argues that this flexibility is a reflection of our ability to select a strategy that will maximize fitness payoff within a given set of environmental circumstances.
Evolutionary psychology predicts that men should bias investment of time and other resources in favour of their own children. These diagrams (adapted from Daly & Wilson (Homicide, New York, Aldine, 1988) show that step children are at greater risk of child abuse and murder, than children living with both their natural parents. These tragedies have been interpreted as a maladaptive side effect of a universal psychological mechanism. You should note that the actual numbers of children murdered by step parents is extremely low. Evolutionary psychologists are not arguing that step parents are 'programmed' to kill step children. What they are saying is that we do have a bias to care for our own children, but that this mechanism can become distorted under certain circumstances.
When a baby is born, relatives and friends invariably comment on how the child resembles other members of the family - the 'he has his father's chin' syndrome. Christenfield and Hill (1995) report that strangers presented with a picture of a one year old and photographs of the child's mother, father and unrelated adults, spotted the child's father at above chance levels, but were unable to identify its mother. An evolutionary explanation of this result would be that a child's facial characteristics inherited from the father are preferentially expressed to reassure daddy that the child is his.
Source: Diamond, The Third Chimpanzee , Harper, New York, 1992
|Except in cases of rape
and forced marriages, women decide who fathers their children. In
contrast, men have relatively little control over this important aspect
of reproductive success. Human female fertility is a 'silent' event, so
men can never be sure that they have fathered the children born to
In orang-utans and gorillas there is a marked difference in size between males and females. In these animals the male is much larger than the female. In contrast, there is very little sexual dimorphism in the sizes of chimpanzees and humans. Orang-utans and gorillas tend to form polygynous groups - one dominant male with a 'harem' of females that he mates with and protects from other males. Human males cannot rely on physical strength to prevent other males mating with their partners.
Consequently attempts to restrict access to a partner's sexual favours is a universal human male behaviour. Marriage, sexual jealousy, and violence by cuckolded males are viewed by evolutionary psychologists as examples of 'mate guarding' .
Mechanisms may have evolved in the human male that reduce the possibility that another man has fertilized their partner's eggs (coloured pink in the diagram). One of these mechanisms is sperm competition in which the man produces a superabundance of sperm (coloured blue) to reduce the chance that his partner is fertilized by the sperm from another man (coloured yellow) that she has copulated with in his absence.
An alternative explanation for this finding ( see Alcock, op. cit . p 628) would be that men who spend time away from their regular partners might have more contact with women who could be potential mating partners. Sperm production increases to cope with these opportunities. This could potentially increase the man's reproductive success.
The large size of the human testes may be adaptation to produce a large quantity of sperm to increase the chances that a man is the father of the children produced by his mate. The adaptive value of the relatively large human penis is unknown.
These results can be interpreted in terms of evolutionary psychology.
According to Buckle et al (1996), over 90% of divorces in England and Wales between 1974 and 1989 were initiated by women under 25 years old. The statistics show that divorces amongst young couples is more likely to be initiated by the wife, but as the couple gets older the husband becomes more likely to initiate divorce proceedings. The evolutionary explanation for this would be that a young woman who realizes that she has made a mistake needs to get out of the relationship as quickly as possible so that she can have children whilst she is still young enough with another partner. In contrast because men can continue to father children until they are at least 65, older men can divorce and raise a family with a new younger partner.
Source: Buckle et al , 1996
In an extremely controversial book Thornhill and Palmer have argued that rape can be explained in terms of evolutionary psychology. The most controversial aspect of their thesis is that men rape because of sexual desire, and not because they want to control and dominate women - the explanation put forward by the feminist writer Susan Brownmiller in 1975.
Thornhill & Palmer view rape as a way in which some men can enhance their inclusive fitness . They view womens' reaction to rape as a reaction to a threat to their inclusive fitness. They argue that
Note that this is an explanation of rape, not a justification for it.
The authors present two hypotheses about the link between rape and human evolution:
The diagram is redrawn from Thornhill &Thornhil l, Ethology and Sociobiology , 4, 137-173, 1983.
Professor Sir Magdi Yacoub - the world renowned heart surgeon surrounded by his team
I have put the phrase - Mother Love - in quotations to emphasise that the equivalent male phrase is 'A father's love for his child' rather than 'Father's love'. There is no special phrase to describe the love received from uncles, aunts and grandparents. Perhaps mother's love is special because only she is absolutely certain that a child will benefit her inclusive fitness.
The diagram shows the extent to which we are related to our close relatives in terms of a shared genetic inheritance. It has been suggested that altruism involves a cost-benefit tradeoff : We will help a distant relative if the cost to us is low, whereas we will endure greater cost for a close relative.
Contributions to charity have been explained in this way. For example, appeals for natural disasters in foreign countries often stress the great benefit to complete strangers if we make a relatively small contribution.
Many charities give small badges to people who make a contribution - this could be an example of capitalising on reciprocal atruism. People who are judged as being helpful may themselves benefit from being helped by other people. Of course the symbol may simply be a way of advertising yourself as a 'good-provider'
Desmond Morris (1977)
explains war, patriotism and other extreme forms of self-sacrifice in
terms of our evolutionary past in which we lived in tribes where
everyone was genetically related to some extent.
Up to now we have emphasized the role of stable , evolved, universal factors in controlling reproductive behaviours. But there is evidence that mate choice may be less stable than suggested so far.
Galef (1995) conduct an interesting experiment which appears to show social learning in a group of rats - what we would call the development of a ' culture '.
Rats were given two identical foods which only differed in flavour by the addition of either cayenne pepper or Japanese horseradish.
This was a complex experiment and I am only going to describe the results from one experimental treatment.
Rats were trained in groups of 4 to prefer horseradish by making them slightly ill after eating the food flavoured with cayenne pepper. The diagram shows a decline in the the amount of cayenne flavoured food eaten over the 14 days of the experiment.
No surprise there, except that the majority of rats in the experiment had never experienced illness after eating cayenne flavoured food. They had acquired the behaviour from rats 'in the know'.
If you examine the identification letters of the rats taking part in the experiment you will see that - starting on day 5 - the four original rats were replaced - one each day - by a new rat that had never been made ill after eating cayenne. By day 8 all the original rats had left the study , but their experience lived on. Indeed by day 11 there wasn't a single rat remaining in the study who had ever been in contact with a rat from the original group of 4 rats who had experienced illness after eating cayenne. Spooky!
One explanation is that rats eat what they smell on their friends. These rats smelt horseradish rather than cayenne on each other. Therefore the tendency to eat horseradish was passed on from rat to rat. Remember that rats - because of their scavenging way of life - need to be very careful about what they eat to avoid being poisoned by decomposed food. "If you can smell it on your friend, it must be OK, because it didn't kill him."
What has this got to do with mate choice? Westneat et al (2000) build on Galef's work and review research investigating the possibility that a female's choice of mate can influence the choices of those around her. It is extremely difficult to separate out competing hypotheses in this research area. For example, male behaviour can change after mating, and this may increase the attractiveness of the male to the female who has observed him mate. Similarly watching mating behaviour may affect the observer's willingness to mate.
One possibility in humans is that a preference for a particular type of mate is learnt as we grow up. Our parents, friends and relatives give use good - or bad - examples of parental behaviour . Thus we may favour relationships with - or without - the characteristics of adults that we have observed during childhood.
Young men seem quick to label some young girls as 'slags' or 'sluts' on the basis of their supposed promiscuity. From what we know about the effect of paternal uncertainty. Perhaps this aspect of 'male culture' can be understood in terms of males concerns over paternity mate choice
Adaptation :The gradual accumulation of inherited characteristics across generations, that give living organisms the best chances of surviving and reproducing in their environment (ie. characteristics that confer high inclusive fitness). The underlying mechanism of evolution by natural selection.
Altruism : disinterested and selfless concern for the well-being of others. Altruism has a fitness cost for the benefactor and a fitness benefit to the recipient.
Darwinism : theory of evolution driven by natural selection. Researchers who study Darwin's theories of evolution are often referred to as Darwinists.
Evolution : comes from the Latin word meaning the 'unrolling of a scroll'. Refers to the adaptive change that occurs over many generations. A change in the gene pool across generations. Scientists believe that over millions of years, simple organisms have developed into more complex ones, each better adapted to its environment that its predecessor. Charles Darwin proposed a means of evolution called natural selection, or the 'survival of the fittest'.
Evolutionary Psychology: a field of psychology concerned with the adaptive value of human behaviours. Uses knowledge and principles drawn from evolutionary biology.
Evolutionary Fitness: the ability of an organism to cope with environmental challenges, and to successfully hand on genes. Natural selection can also be said to occur because of difference in fitness within a population.
Fitness: often measured as the number of offspring produced by an individual that survive and reproduce themselves. Fitness reflects the genes contributed by an individual to their descendants. Humans effect their fitness through successful mating- called direct fitness , or by helping relatives (with whom they share genes) to reproduce - indirect fitness .
Inclusive fitness = direct fitness + indirect fitness
Group Selection : a theory put forward by Wynne-Edwards in 1962 that evolution by natural selection occurs on the scale of the group , as opposed to the individual. According to this theory, groups or species in which individual members are prepared to sacrifice their own welfare, and even life for the benefit of the group, are less likely to become extinct than a group in which individuals put their own interests first. This theory is no longer as popular as it was in the 1960's and 70's.
Man is used on this page to refer to male and female humans.
Monogamous : having only one sexual partner, or mate, at any one time.
Natural Selection : difference in reproductive capability. Thought to be the main process of evolution by natural selection, whereby organisms that are better adapted to their environment tend to survive and produce more offspring. The most common process of natural selection is to remove 'unfit' variants of an organism as they arise via mutation of genes across generations, producing new organisms with a different genetic makeup. First proposed by Charles Darwin, as outlined in his book, The Origin Species. Often referred to as 'survival of the fittest'.
Parental investment: in any species the parent (male or female) that invests the most time, energy, and resources on its offspring will be the choosier mate
Sexual Selection: sexual selection is natural selection operating on characteristics that contribute to an organism's mating success but not necessarily to their survival, eg. the male peacock's lurid tail. Can occur in two ways, namely: certain characteristics or traits may increase the ability to compete with individuals of the same sex for access to mates, while other traits increase the ability to attract individuals of the opposite sex.
Sociobiology : the scientific study of the biological (especially evolutionary and ecological) aspects of the social behaviour in animals and humans.
View the PBS video "Sweaty T-Shirts and Human Mate Choice" which is available online (if necessary, borrow headphones from the technicians office ) and consider the following points:
It strikes me that some of the most interesting questions about human behaviour tend to involve things we take for granted. For example "Why are we afraid of the dark?" The 'common sense' answer is because we can't see well in the dark. But actually it's quite rare to go into the countryside at night and not be able to see well enough to move about relatively easily. Nevertheless going alone at night into the countryside can be a really scarry experience. The film "Blair Witch Project" may evoke memories of camping and being frozen with fear after listening to the rustling of leaves or animals in the night.
Here are some interesting questions posed by Gregory Carey (1998 chapter 15 ) which is available online about human behaviours that we take for granted, or invite common sense answers:
There is a very provocative section at the end of this video in which Moller & Thornhill give an evolutionary explanation for sex discrimination in academic jobs. You may want to consider their arguments in the light of Richard Dawkins lecture: " Our big brains can overcome our selfish genes " given at the Royal Institution, in London 12 February 2002